Eoraptor was a small, lightly-built dinosaur that walked on two long legs. It was about 3 feet long (1 m); it had light, hollow bones, a long head with dozens of small, sharp teeth, and five fingers on its grasping hands (two of the fingers on each hand were very small).

The fossil was found in the Ischigualasto Formation in the Argentine. This contains some of the oldest known dinosaur remains. They are of top quality, number and importance. It is the only place in the world where nearly all of the Triassic is represented in an undisturbed sequence of strata. What is now badlands was then a volcanically active floodplain dominated by rivers, with a strongly seasonal rainfall.

The teeth of Eoraptor are of two types. There are serrated, recurved teeth in the maxillae (upper jaws), like the teeth of theropods, and leaf-shaped teeth in the dentary (lower jaw), like the teeth of basal sauropodomorphs.[4]